Apparatus for reading from or writing to optical recording media having means of disk type identification

ABSTRACT

A device for reading or writing on optical recording media with disk type recognition capability has an optical scanning device and a focus regulating circuit. The arrangement provides rapid and reliable recognition of the recording medium type inserted into the device. A further inventive aspect provides a corresponding process. These inventive aspects are attained by the disk type recognition capability which includes a mirror signal generator, a threshold value generator, a counter and an evaluation unit. The process is based on the utilization of a mirror-signal value of the device for disk type recognition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 09/508,804 filed Mar. 16, 2000.

BACKGROUND OF THE INVENTION

1. Field Of The Invention

The present invention relates to an apparatus for reading from and/orwriting to optical recording media which has a disk type identificationmeans for identifying the type of recording medium, and also to acorresponding method.

2. Prior Art

An apparatus of this type is disclosed in U.S. Pat. No. 5,414,684. Inthis known apparatus, in order to identify the type of recording mediuman attempt is made to read the list of contents, the so-called TOC orTable of Contents. If it is not possible to read the TOC, then one or anumber of attempts are made to read information at one or a number ofother locations on the recording medium. The type of optical recordingmedium is inferred from the success or lack of success of theseattempts.

What is disadvantageous about the known apparatus is that a completeset-up operation has to be performed for each attempt to readinformation. This operation includes, inter alia, the closing of focusregulating circuit, track regulating circuit, drive regulating circuitand the like. This procedure is relatively complicated andtime-consuming.

SUMMARY OF THE INVENTION

In a first arrangement an apparatus having an inventive disk typeidentification means is able, within a short time, to reliably identifythe type of the recording medium inserted into the apparatus. A furtherinventive arrangement specifies a corresponding method for disk typeidentification.

According to the invention, these objects are achieved by means of thefeatures specified in the independent claims. Advantageous developmentsthereof are specified in the dependent claims.

According to the invention, the disk type identification means has amirror signal detector, a threshold value generator, a counter and anevaluation unit. This has the advantage that rapid identification of thetype of recording medium is attained. The disk type identification meanshas elements with a relatively simple function which enable informationabout the type of disk to be obtained even when the recording mediumcannot yet be read even though the focus regulating circuit is closed.The mirror signal is a signal which assumes different values if thescanning means is scanning an information track or a region between twoinformation tracks. In this case, the region located between twoinformation tracks may be free of information, but it may also carryinformation, for example control information or information of a kindwhich corresponds to that of the information tracks.

According to the invention, an input of the mirror signal detector isconnected to an output of the scanning means and a further input isconnected to the threshold value generator, and a counter is connectedto an output of the mirror signal detector and to an input of theevaluation unit. In the case of this advantageous combination of theindividual elements, the threshold value generator specifies a thresholdvalue for the formation of the mirror signal. The counter counts theoccurrence of specific states of the mirror signal, for example thenumber of high or low states, corresponding transitions, zero crossingsor the like. The evaluation unit evaluates the counter reading for thepurpose of determining the type of recording medium.

A further advantageous aspect of the invention provides a layerthickness identification means. This advantageous layer thicknessidentification means supplies an additional criterion by means of whichspecific settings of the apparatus are suitably preselected toaccelerate the identification of the type of disk. In addition or as analternative, the additional criterion also serves as a criterion for theidentification of the type of disk, thereby accelerating theidentification or increasing its reliability. The layer thicknessidentification means serves for determining the thickness of aprotective layer which is superposed on an information-carrying layer ofthe recording medium.

A further aspect of the invention provides for the apparatus to have aspacing identification means for determining the spacing of differentlayers of the recording medium from one another. This additionalcriterion also contributes to accelerating and/or to increasing thereliability of the identification of the type of disk. In this case, thevarious levels are advantageously two or more information layers.However, it is also likewise within the scope of the invention for thelayers to be other layers which are present in the structure of theoptical recording medium and can be detected.

An inventive method for identifying the type of optical recording mediumhas the following steps: aa) focusing onto an information layer of therecording medium; bb) setting a threshold value for the generation of amirror signal; cc) counting transitions of the mirror signal; dd)determining the type of the recording medium using the count. Thismethod has the advantage that a tracking mode and signal identification,for example, by reading of the information stored on the recordingmedium, are not necessary, which enables the type of disk to beidentified rapidly. As soon as the type of recording medium has beenidentified, apparatus settings which are in accordance with this type ofrecording medium, in particular focus, tracking and other regulatingcircuits, are selected. As a result, the start-up phase, for example,the time from the insertion of the recording medium into the apparatusor from the issuing of a start command until the beginning of playbackor recording, can be kept short. Consequently, the waiting time for theuser is advantageously shortened.

According to the inventive step dd), the recording medium is determinedas being associated with an nth type if the count lies in an nth rangeof values, where n is an integer. This has the advantage that, ifappropriate, a multiplicity of different types of recording media can beidentified without the counts necessarily having to be exact. In thesimplest case a check is made to see whether the count is greater orless than a limit value. This limit value is regarded as the limitbetween two ranges of values. In the extreme case, a single type ofrecording medium is identified for example by virtue of the fact thatthe count is greater than a limit value. For n=2, by way of example, therecording medium is determined as being associated with a first type ifthe count lies between zero and a first value m1, while it is determinedas being associated with a second type if the count lies between asecond value m2 and a third value m3. In this case, it is perfectlypossible for the start value m0 also to be a value other than zero, orfor the first value m1 and second value m2 to be identical. The sameapplies correspondingly to three or a larger number of disk types to beidentified.

A advantageous aspect of the method provides for the scanning beam ofthe scanning means of the apparatus to be moved across a region of therecording medium which is larger than a region which corresponds to themaximum eccentricity that occurs. This has the advantage that more rapidand more reliable identification is made possible by the large number,achieved as a consequence, of information tracks crossed by the scanningbeam. In this case, the eccentricity includes both theproduction-dictated eccentricity of the recording medium, that is to saythe circular or spiral information tracks thereof which are not centredexactly with respect to the axis of rotational symmetry, andeccentricity engendered by operation, for example due to inexactcentring of the recording medium in the apparatus. The eccentricity issubject to tolerance ranges which, in practice, are generally notexceeded and which serve here as a lower limit for the induced movementof the scanning beam.

A further advantageous refinement of the invention provides for stepsbb) to cc) to be performed a number of times, a different thresholdvalue being set in each case in step bb). This refinement has theadvantage that a larger number of different types of disk can beidentified relatively rapidly. A further advantage is that, incombination with a plurality of ranges of values, a small number ofpasses suffices to be able to distinguish a large number of differenttypes. Furthermore, counterchecking by means of different passes makesit possible to increase the checking reliability relatively rapidly.

In addition the invention provides, after the type of recording mediumhas been determined, for a check to be made to see whether focusing ontoa further information layer is possible. This has the advantage that thepresence of a multilayer recording medium is detected with apparatussettings which are adapted to the recording medium, which reduces thetime that elapses until complete identification of the disk type hasended, and also enables multilayer recording media to be identified.

According to yet a further aspect of the invention, the method accordingto the invention is first of all utilized for identifying the type ofinformation layer onto which the optical scanning unit effects focusing,then the settings of the apparatus are adapted to the layer type thathas been determined, information is read from the said information layerand the type of recording medium is determined from the informationread. This method has the advantage that the identification operation isagain shortened, since it is not necessary to search for furtherinformation layers if the presence and, if appropriate, the type offurther layers can be identified from the information read from thefirst information layer.

An advantageous variant of the invention provides for the mirror signaldetector to have at least one element which is variable as a function offrequency. This has the advantage that an element which is variable as afunction of frequency can be adaptively matched in terms of itsproperties to the track crossing frequency during operation, with theresult that interfering influences which occur in certain frequencyranges are compensated for or minimized in a frequency-selective manner.The mirror signal detector generates a mirror signal indicating whetherthe scanning means is scanning a data track or is located between twodata tracks. To that end, the high-frequency signal read from the diskis considered. For example if it has a high degree of modulation thescanning means is scanning a data track, whereas it is only weaklymodulated if the scanning means is scanning between two data tracks. Itis the case at high track crossing frequencies that the differences inmodulation between data track and the interspace between two data tracksare only very small. Slightly modulated input signals occur for examplein the case of high-density recording media. In that case, when aninformation track is traversed, the intensity of the high-frequencysignal decreases, in some instances, only by 20% in comparison with thetraversal of the reflective region lying between the information tracks,whereas this value is approximately 65% in the case of conventionalcompact discs. The apparatus advantageously has a control device whichinfluences the threshold value-forming unit and also a track regulator.This has the advantage that in order to determine the type of opticalrecording medium, the track regulator is inactivated and the thresholdvalue-forming unit is set to a fixed threshold value. The effect ofswitching off the track regulator is that information tracks of therecording medium are traversed. Depending on the type of recordingmedium, it is possible to establish a mirror signal with regard to asuitably set threshold value or this is not possible, and from this aconclusion is drawn regarding the type of optical recording medium. Theaveraging is likewise effected as a function of the frequency of themirror signal. This has the advantage that in the event of ahigher-frequency signal, the average value is also formed at a higherfrequency in order to be matched as quickly as possible to a possiblyaltered signal intensity, as occurs e.g. in the case of recording mediahaving a high storage density, as specified above.

Furthermore, provision is made for an upper and a lower threshold valueto be used instead of a single threshold value, the mirror signal beingset to a first value, for example the value 1, when the upper thresholdvalue is exceeded, and being set to a second value, for example thevalue 0 when the lower threshold value is undershot, its value otherwisebeing maintained. This has the advantage that the value of the mirrorsignal does not fluctuate to an unnecessarily great extent in thetransition region between the two values, i.e. becomes smoother.Hysteresis prevents the value of the mirror signal from jumping back andforth in the transition region between the two values. As a result, thefrequency determination of the mirror signal also becomes even moreaccurate and the quality of the method according to the invention isincreased.

Yet a further advantageous variant of the inventive method includesspecifying a certain threshold value and checking whether or not amirror signal can be established with regard thereto. This has theadvantage that the type of recording medium can be determined by meansof a mirror signal detector which is present in any case, i.e. withoutany additional outlay. If a mirror signal can be established, then afirst type of recording medium is being scanned; if, on the other hand,a mirror signal cannot be established, then a second type of recordingmedium is involved. The different types of recording media differ, forexample, in terms of their track arrangement, the size of the trackwidth or of the track spacing, as is the case for example, withconventional CDs and recording media having a high storage density, suchas DVDs.

In an advantageous manner a plurality of different threshold values aretested one after the other. This has the advantage of increasing thenumber of different types of recording media that can be identified.Consequently, types which vary only slightly in terms of theirproperties can also be distinguished using the mirror signal which canbe determined with regard to different threshold values. For example,write-once, write-many and non-writable optical recording media differ,in some instances, only slightly with regard to the threshold valuewhich is suitable for forming the mirror signal, yet they can beidentified reliably by means of the method according to the invention onthe basis of the plurality of threshold values used. The invention issuitable for distinguishing different types of recording media from oneanother, such as, inter alia, CD, CD-R, CD-RW and DVD, DVD-RAM andothers.

According to the invention, information tracks of the recording mediumare traversed during the implementation of the method steps, this beingeffected in the simplest case by switching off a track regulator andutilizing eccentricity of the recording medium or its mounting in theapparatus. It is particularly advantageous to actively implementtraversal of information tracks. This has the advantage that theconditions for generating a mirror signal are always met and,consequently, even an absent mirror signal can be ascribed unambiguouslyto the type of recording medium.

Further advantages of the invention are evident from the followingdescription of advantageous exemplary embodiments. It is understood thatthe invention is not restricted to the exemplary embodiments describedherein.

BRIEF DESCRIPTION OF THE DRAWINGS

In the figures:

FIG. 1 shows a diagrammatic illustration of an apparatus according tothe invention,

FIG. 2 shows a diagrammatic illustration of an exemplary embodiment ofan apparatus according to the invention,

FIG. 3 shows a diagram of typical signals occurring in an apparatusaccording to the invention,

FIG. 4 shows a block diagram of an apparatus according to the invention,

FIG. 5 shows a flow diagram of a method according to the invention,

FIG. 6 shows a flow diagram of a variant of the method,

FIG. 7 shows a flow diagram of a further variant of the method.

DETAILED DESCRIPTION

FIG. 1 shows a schematic illustration of the disk type identificationmeans of an apparatus according to the invention. A high-frequency datasignal HF, which is output by the scanning means 5 (not illustratedhere), is fed to a threshold value-forming unit 12, 14 and a mirrorsignal-forming unit 13. The threshold value-forming unit 12, 14generates a threshold value TH, which is fed to the mirrorsignal-forming unit 13. In an advantageous variant, a plurality ofthreshold values are formed, which are in this case specified as anupper threshold value UTH and a lower threshold value LTH. The mirrorsignal MIR generated by the mirror signal-forming unit 13 is fed to acounter, which is also referred to as frequency counter 15 in the textbelow. The functions of the threshold value-forming unit 12, 14 and themirror signal-forming unit 13 are explained in more detail below.

The frequency counter 15 counts edges (positive in the exemplaryembodiment) of the mirror signal MIR and, after a period of time whichis determined by an externally prescribed clock signal, forwards thecount Z to a logic block 16, which serves as an evaluation unit. Acontrol unit 26 can both receive information from the logic block 16 andforward information to the said logic block. It is connected to a memoryM and to the threshold value-forming unit 14. In order to determine thetype of recording medium, the control unit 26 specifies to the thresholdvalue-forming unit 14 a threshold value TH to be set. The latter doesnot generally correspond to the adapted threshold value for thecurrently inserted recording medium. The consequence of this is that themirror signal MIR that is generated in response is well performed to agreater or lesser extent, this being manifested for example in thenumber of countable edges. The count Z then assumes a larger or smallervalue.

In the simplest exemplary embodiment, the count Z is compared with acomparison value ml in the logic block 16. If the count lies below thevalue ml, then the presence of a first type of recording medium, forexample a CD, is indicated by means of an output signal T1, while thepresence of a second type, for example a DVD, is otherwise indicated.After the type Tn of recording medium has been determined, thespecification of the threshold value TH is cancelled and the latter isthen adapted, as described further below, for normal operation.

Refinements of the invention provide for the control unit 26 tosuccessively specify different specifications for the threshold value THto the threshold value-forming unit 14, to evaluate the correspondingoutput signals of the logic block 16, to thereupon determine a disk typeTn from a multiplicity of disk types and to output a correspondingoutput signal Tn. The memory M serves for storing specification values,interim results, results or further parameters. The logic block 16 can,as described further below, also perform even further functions.

FIG. 2 shows a diagrammatic illustration of a mirror signal detector 1of an apparatus according to the invention. An envelope signal E isapplied to its input and the mirror signal MIR is present at its output.The envelope signal E is generated from a digitized high-frequency DHFby means of an envelope detector 2. In the exemplary embodiment, a peakvalue detector with a slowly forming hold value is used for thispurpose, as is indicated in the block illustration of the envelopedetector 2. The high-frequency DHF is generated by means of ananalogue-to-digital converter 3, to whose input a high-frequency datasignal HF is applied.

FIG. 4 shows a schematic block diagram of a device according to theinvention. An optical recording medium 4, which has diagrammaticallyindicated, concentrically or spirally arranged information tracks 25, isscanned by means of a light beam 6 generated by a scanning means 5. Thelight beam 6 is in this case reflected from the optical recording medium4 and passes to detection elements of the scanning means 5, where it isconverted into a data signal HF and into error signals, specified astrack error signal TE and focus error signal FE here by way of example,and output by the scanning-means 5. The data signal HF is converted intoa digitized high-frequency signal DHF by means of theanalogue-to-digital converter 3, which signal is fed to the mirrorsignal detector 1, on the one hand, and to a demodulation stage 7 (onlysuggested here), on the other hand. The demodulation stage 7 serves todemodulate the data signal, which is modulated for recording on therecording medium 4, and to output it as audio signal or demodulated datasignal. The envelope detector 2 described with regard to FIG. 1 is notillustrated separately in FIG. 4; it is part of the mirror signaldetector 1, for example. The track error signal TE and the focus errorsignal FE are also digitized by means of an analogue-to-digitalconverter 3′, the digitized track error signal DTE is converted into asignal DTE′ in a conditioning stage 8 and forwarded to a signalprocessing stage 9. The latter also receives the mirror signal MIRoutput by the mirror signal detector 1, logically combines the twosignals and outputs a signal to a track regulator 10. The latterforwards an actuating signal to the scanning means 5, in order todisplace the latter in the radial direction with regard to the opticalrecording medium 4. In the event of a normal read-out of the recordingmedium 4, the radial displacement serves for tracking the light beam 6on an information track 25 of the optical recording medium 4, whereas inthe event of a search operation, the radial movement of the scanningmeans 5 serves for the traversal of a predetermined number ofinformation tracks 25. The number of tracks traversed may be determinedin this case, for example, by counting the positive edges of the mirrorsignal MIR. The result is used to displace the scanning means 5correspondingly radially, so that the track sought is reached in themost exact manner possible.

The digitized focus error signal DFE is fed to a focus regulating unit28, which outputs a signal for driving optical elements of the scanningunit 5 to the latter. This is done in such a way that the light beam 6is focused onto the information layer of the recording medium 4.According to a variant of the invention, the focus regulating unit 28has a further function, in a special operating state, of moving thefocal point of the light beam 6 in the axial direction of the recordingmedium 4, and of evaluating the values of the focus error signal FE thatoccur in the process. The layer thickness of the protective layer whichcovers the information layer is determined from the presence and therelative spacings and values of maxima in the focus error signal FE. Ifthe recording medium is a multilayer recording medium, the presence andthe respective spacing of a plurality of layers from one another arealso determined. The focus regulating unit 28 thus serves as layerthickness identification means or as spacing identification means.

The control unit 26, which serves to establish the type of opticalrecording medium 4, for example CD or DVD, is illustrateddiagrammatically as an independent block in this figure. An output ofthe control unit 26 is connected to the mirror signal detector 1 inorder to set a specific threshold value TH, as described further below.A further output of the control unit 26 is connected to the trackregulator 10 in order to switch this regulator off or, according toanother variant of the invention, in order to control this regulator insuch a way that information tracks 25 are actively traversed. An outputof the mirror signal detector 1 is connected to an input of the controlunit 26. The type of recording medium currently being scanned isestablished from the signal communicated in this case, if appropriatefrom a plurality of communicated signals buffer-stored in a memory M.

The individual component parts of the mirror signal detector 1 will nowbe explained in more detail with reference to FIG. 2. The envelopesignal E is fed to a digital low-pass filter 11, the cut-off frequencyEF1 of which is variable and is set in accordance with a control signalSL1. In the case of the IIR filter illustrated here, this is implementedin that the system clock signal CLK is divided by a value specified bythe control signal SL1 and the frequency that has been reduced in thisway produces the operating clock of the digital low-pass filter 11. Thelower the operating clock of the low-pass filter 11, the lower, too, isthe cut-off frequency EF1 thereof. The output signal FIL of the filter11 is fed to a mirror signal-forming unit 13 designed as a comparator,for example. According to a first configuration, the mirrorsignal-forming unit 13 in this case compares the signal FIL with athreshold value TH. If the value of the signal FIL lies above thethreshold value TH, then the value of the mirror signal MIR is set to afirst value, in this case to 1; if, on the other hand, the value of thesignal FIL lies below the threshold value TH, then the mirror signal MIRis set to a second value, in this case to the value 0.

According to a second variant, the mirror signal-forming unit 13compares the signal FIL with an upper threshold value UTH and a lowerthreshold value LTH. In this case, the value of the mirror signal MIR isset to 1 if the value of the signal FIL lies above the value of theupper threshold value UTH, and it is set to 0 if the value of the signalFIL lies below the lower threshold value LTH. The value of the mirrorsignal MIR remains unchanged as long as the value of the signal FIL isbetween the upper threshold value UTH and the lower threshold value LTH.

One variant consists in keeping the threshold value TH or the upperthreshold value UTH and the lower threshold value LTH constant, or notchanging them as a function of frequency. It is advantageous, however,to adapt the threshold values TH or UTH and LTH as a function offrequency. A second digital low-pass filter 12 is provided for thispurpose, which filter is likewise designed as an IIR filter. Asdescribed with regard to the filter 11, the cut-off frequency EF2 of thefilter 12 is varied as a function of frequency by reducing the systemclock signal CLK by a factor specified by a control signal SL2 to formthe operating clock of the filter 12. From the input signal of thefilter 12, the signal FIL, an average value free from higher-frequencydeviations is formed, by virtue of a suitably selected filtercharacteristic, and output as threshold value TH. The filter 12 thusacts as an averaging unit. The threshold value TH is fed directly to themirror signal-forming unit 13 according to the first variant describedabove, this being illustrated by a dashed line in FIG. 2. It isadvantageous, however, to feed the threshold value TH to a thresholdvalue-forming unit 14, which forms the upper threshold value UTH and thelower threshold value LTH from the threshold value TH by means of anupper hysteresis value UHY and a lower hysteresis value LHY, for exampleby addition or subtraction.

The mirror signal MIR is both output and fed to a frequency counter 15within the mirror signal detector 1. This frequency counter operateswith a fixed clock signal CL1, which can be adapted in a device-specificmanner but is constant during operation. In the exemplary embodiment,the frequency counter 15 is designed as an 8-bit counter whose overflowforms the output signal. If the output signal of the frequency counter15 is to have a higher frequency, then provision is made for outputtingthe value of the highest or of the second-highest counter bit. Any otherbit is also suitable for this purpose, depending on the desiredfrequency. The output signal of the frequency counter 15 forms the inputsignal of a logic block 16, which sets the control signals SL1 and SL2in accordance with its input signal using specified threshold values, inaccordance with a specified algorithm, or using a stored table.

The exemplary embodiment described enables a correct mirror signal MIRto be obtained even when an optical recording medium 4 having a highstorage density is used, such as a DVD, for example, and in the event ofhigh track crossing frequencies. In this case, the envelope signal E iscompared with a threshold value TH in order to generate the mirrorsignal MIR. Since the envelope signal E is modulated only by about 20%with respect to the maximum value during track crossing in the case ofrecording media 4 having a high storage density, whereas this figure isabout 65% in the case of conventional recording media, such as in thecase of a CD, frequency-dependent adaptive filters 11, 12 are providedaccording to the invention. The frequency dependence in this case beginswith a low cut-off frequency EF1, EF2 at the beginning of a trackcrossing operation in order to suppress high-frequency interferinginfluences lying, for instance, in the frequency range of the trackcrossing frequency at a maximum track crossing speed. As the trackcrossing speed rises, that is to say as the frequency of the mirrorsignal MIR rises, the cut-off frequency EF1 and/or EF2 is increased inorder to allow the frequencies then necessary to pass. Towards the endof the track crossing operation, the cut-off frequency EF1, EF2 isdecreased again. In order to take account of the relatively narrowmodulation bandwidth of the envelope signal E, which is of the order ofmagnitude of only 20%, as described, the second low-pass filter 12 isprovided for the purpose of forming the threshold value TH, which filterreacts rapidly to changes in the amplitude of the data signal HF andthus of the envelope signal E, which may be caused for example byeccentricity of the recording medium 4, by changes in the reflectivity,or by other interfering influences. The low-pass filter 12 is alsoadaptable as a function of frequency. The frequency-dependent adaptationof the filters 11, 12 depends on the track crossing frequency, for whichreason a measure of this frequency is obtained from the period of themirror signal MIR. The envelope signal E is generated by means of theenvelope detector 2 by detection of the peak value and slow falling, asindicated symbolically.

FIG. 3 illustrates the typical profile of a number of signals occurringin the device according to the invention against the time t. The outputsignal FIL corresponding to the filtered envelope signal E is free fromhigh-frequency interfering superpositions. The signal of the thresholdvalue TH which is obtained by low-pass filtering is derived from thesignal FIL. It is modulated to a lesser extent than the signal FIL andhas steps on account of the internal clock of the filter 12. The mirrorsignal MIR, which is illustrated as inverted mirror signal {overscore(MIR)} in FIG. 3, is formed in the mirror signal-forming unit 13 bycomparison of the signals FIL and TH. {overscore (MIR)} is at a value“high” or 1 when the signal FIL is below the threshold value TH, whilethe inverted mirror signal {overscore (MIR)} is at “low” or the value 0when the signal FIL is above the threshold value TH. The arrow 21indicates the period length of the mirror signal MIR, this period lengthyielding the track crossing frequency which is utilized, in turn, foradaptation of the filters 11 and 12.

The method, employed in the exemplary embodiment, for thefrequency-dependent formation of the parameter mirror signal MIR isdescribed with reference to FIG. 2. In a first method step a), theenvelope signal E is formed from the data signal HF by means of theenvelope detector 2. It is subsequently filtered, in step b), by meansof the filter 11 taking account of a cut-off frequency EF1. The filteredenvelope signal FIL is then compared, in step c), with a threshold valueTH by means of the mirror signal-forming unit 13. The parameter mirrorsignal MIR is set, in step d), to a first value if the filtered envelopesignal FIL lies above the threshold value TH, and to a second value ifit lies below the threshold value TH. In step e), the frequency of themirror signal MIR is determined by means of the frequency counter 15.The value of the cut-off frequency EF1, EF2 is changed as a function ofthe frequency of the mirror signal MIR in step f). As long as the trackcrossing operation has not yet concluded, branching to the first stepsubsequently takes place in step g), otherwise the method is ended. Thethreshold value TH is formed by averaging the envelope signal E by meansof the filter 12. This averaging likewise takes place as a function ofthe frequency of the mirror signal MIR, in this case by correspondingvariation of the control signal SL2. An upper threshold value UTH and alower threshold value LTH are formed from the threshold value TH bymeans of the threshold value-forming unit 14. The parameter mirrorsignal MIR is in this case set to a first value if the filtered envelopesignal FIL lies above the upper threshold value UTH, and to a secondvalue if it lies below the lower threshold value LTH, otherwise thepreceding value of the parameter mirror signal MIR is maintained.

FIG. 5 represents a flow diagram of an exemplary embodiment of a methodaccording to the invention for identifying the type of an opticalrecording medium. The principle behind this method consists in utilizinga parameter mirror signal MIR in a device for reading from and/orwriting to optical recording media 4. To that end, step aa), first ofall focusing onto the information layer of the recording medium 4 iseffected. This is done by means of the focus regulating unit 28 in amanner known to the person skilled in the art. In the focused state, thevalue of the focus error signal is almost zero; the focusing operationis therefore indicated by FE→0 in this case. In step bb), a thresholdvalue TH for forming the mirror signal MIR is specified. According toone variant; provision is made for performing step bb) repeatedly. Inthis case, a threshold value THi is specified during the ith pass. Inthe text below, the index i is specified even when repeated performanceis not involved. The counter 15 forms a count Zi from the mirror signalMIR formed by means of the threshold value THi. This is specified instep cc). The type Tn of recording medium 4 is determined from the countor the counts Zi in step dd) or de), respectively. In step dd), a simplevariant is specified according to which the nth type Tn is involved ifthe count Zi lies within a range of values bounded by values m_(n) andm_(n+1). In step de), a more general specification is given by thepresence of the nth type Tn can also be defined by the combination of aplurality of counts Zi.

According to a variant of the invention, after step cc), in step cd) thecount Zi that has been determined is first of all stored, in step ce)the count i is incremented, and in step cf) the method branches to stepbb) as long as a maximum value imax is not exceeded. In this case, thethreshold value THi is changed a number of times, corresponding countsZi are stored and utilized during the concluding performance of step de)for determining the type Tn. A modification provides, after step cc),first of all for a check to be made to see whether a type Tn can beambiguously determined using the information already present, that is tosay first of all for step de) to be executed. Only if it is not yetpossible to determine the type does the method then branch to step cd),otherwise the process ends.

A further variant provides, in step df), for identification of the layerthickness of the protective layer covering the information layer, or ofseparating layers which, if appropriate, separate a plurality of layersof the recording medium 4. The layer thickness determined in the processserves as an additional item of information, which, for the sake ofsimplicity, is likewise designated as a count Zi, for determining thetype Tn in step de). Step df) is preferably coupled to the or with thefocusing operation from step aa).

According to a further variant, after step aa) and before step bb), aperiodic movement of the scanner 5 in the radial direction is started.This is specified in step ab). The periodic movement is ended as soon asthe type of recording medium has been established.

FIG. 6 represents a flow diagram of a further exemplary embodiment of amethod according to the invention. In this case, steps aa) to de)correspond to those described with regard to FIG. 5, with the differencethat in this case the type TIn of the information layer onto whichfocusing is detected is determined. Once the type TIn is known, in stepee) the apparatus settings, in particular those for track, focus andother regulating circuits, are adapated to the type TIn of informationlayer determined. In step ff) information is read from the currentinformation layer and the type Tn of recording medium 4 is determinedusing the information read and, if appropriate, the type TIn alreadydetermined. In general, the type Tn can already be gathered from theinformation read, otherwise it is determined, for instance using astored table or a suitable algorithm, from the information read.

FIG. 7 represents a flow diagram of an exemplary embodiment of a methodaccording to the invention for identifying the type of an opticalrecording medium. The principle behind this method consists in utilizinga parameter mirror signal MIR in an apparatus for reading from and/orwriting to optical recording media 4. To that end, in step w), athreshold value THi is specified which, in step c) is compared with anoutput signal FIL derived from the data signal HF, from which the mirrorsignal MIR is formed in step d). In step e), a check is made to seewhether a mirror signal MIR can be formed with regard to the thresholdvalue THi, that is to say whether the value of the mirror signal MIRremains constant or changes with a frequency Fi, which may very wellvary. From this information, in the simplest case Fi=0 or Fi≠0, the typeof recording medium 4 is determined. In this case, the setting of thethreshold value THi is initiated by the control unit 26, whichcorrespondingly drives the threshold value-forming unit 14 of the mirrorsignal detector 1, receives from the latter the frequency Fi or, asdescribed above, a count Zi and determines the type Tn.

The following method steps are advantageously implemented in addition tothe steps described above, but are not all absolutely necessary for themethod according to the invention. In step v), a counter value i is setto a start value imin. In the normal case, imin=1, and the count isrequired only when it is intended to specify more than one thresholdvalue TH. In step w), a threshold value TH is set to a specifiedthreshold value THi in accordance with the count i. Steps a) and b),that is to say the formation of an envelope signal E from the datasignal HF and the filtering of the envelope signal E taking account of acut-off frequency EF1, correspond to the exemplary embodiment describedfurther above. The filtered envelope signal FIL is compared with thethreshold value THi in step c), and in step d) the parameter mirrorsignal MIR is set to a first value, in this case the value 1, if thefiltered envelope signal FIL lies above the threshold value THi, and toa second value, in this case the value zero, if it lies below thethreshold value THi. The frequency Fi of the mirror signal MIR isdetermined in step e). Branching to step a) takes place in step g) if aspecified first time interval t1 has not yet been exceeded. The timeinterval t1 is selected such that steps a) to e) are iteratedsufficiently to enable a meaningful frequency Fi to be established. Thevalue of the frequency Fi is stored in the memory M in step 1) after thefirst time interval t1 has been exceeded. This storage operation can beomitted if only a single threshold value THi is used in the method. Theincrementing of the counter value i by a specified value, in general bythe value 1, in step m) is also necessary only when a plurality ofthreshold values are used. In step n), branching to step w) is effectedas often as until the count i has exceeded a specified end value imax.Subsequently, in step p) the type of recording medium 4 is determinedfrom the frequencies Fi established, it generally sufficing todistinguish between Fi=0 and Fi≠0. The invention guarantees that amirror signal MIR can always be generated by ensuring that informationtracks 25 of the recording medium 4 are traversed at the same time asthe implementation of the method steps. For this purpose, the normaltracking regulating mode of the track regulator 10 is inactivated priorto implementation of the first method step v) and is reactivated at theend of the last step p). During implementation of method steps v) to p),the scanning means 5 is driven in such a way that information tracks 25are traversed, for example by the use of a suitable operating mode ofthe track regulator 10. To that end, the scanning means 5 is preferablydeflected periodically, alternately in the positive and negativedirections.

1. Apparatus for reading from and/or writing to optical recording media, comprising: means for disk type identification including a mirror-signal forming unit and a threshold value forming unit forming at least two of a plurality of possible threshold values; an optical scanning means; a focus regulating circuit; a counter; and, an evaluation unit.
 2. Apparatus according to claim 1, wherein inputs of the mirror signal-forming unit are connected to an output of the scanning means and to the threshold value-forming unit, and the counter is connected to an output of the mirror signal-forming unit and to an input of the evaluation unit.
 3. Apparatus according to claim 1, comprising a layer thickness identification means for determining a thickness of a protective layer covering an information layer of the recording medium.
 4. Apparatus according to claim 1, comprising a spacing identification means for determining a spacing between information layers.
 5. A method for identifying a type of optical recording medium, comprising the steps of: aa) focusing on an information layer of the recording medium; bb) applying ones of a plurality of threshold values for the generation of a mirror signal, some of the plurality of threshold values being unsuitable for generating the mirror signal for at least one type of recording medium; cc) counting transitions of the mirror signal; and, dd) determining a type of recording medium using the count.
 6. The method of claim 5, comprising the step of: providing at least two ranges of count values respectively associated to different recording medium types.
 7. The method of claim 5, wherein said step dd) further comprises: determining the recording medium as being of a type when the count value is in a range of values associated with a type. 